Improved survival in Treg recipients correlate with lower viral load. Viral load (A) and percent viral-free survival (B) of BM only or BM + Treg recipients on day 100 following transplantation. (A) Euthymic and athymic animals that received BM alone or with Tcons and Tregs are killed and organs (kidney, lungs, and liver) are extracted for viral load assessment. Shown is the kidney viral load (log plaque forming units [pfu] per gram tissue) from euthymic mice that received BM only (open symbol) or with Tcon + Treg (filled symbol) on day 0 and infected on day 14, day 30, or day 63, and athymic mice that received BM only (open symbol) or with Tcon + Treg (filled symbol) on day 0 and infected on day 30. Solid lines indicate mean viral load. Dotted line indicates the detection limit of the plaque assay. P = NS for viral load in recipients of BM only vs BM + Tcon + Treg; P = NS and .02, for ● versus ▴, and ▴ versus ■, respectively; P = .04 and .003, for O versus ▵, and ▵ versus □, respectively). (B) Euthymic or athymic animals that received BM alone (open bar) or with Tcon + Treg (filled bar) and were infected on days 14 or 30 or 63 were assessed on day 100 for the presence of virus in the salivary glands, kidneys, liver, and lungs. Uninfected animals in the respective groups served as controls. Data are shown for virus detectable in the kidneys. All thymectomized recipients that survived had detectable viral load. P = NS for survival without virus in BM vs BM + Tcon + Treg animals. In BM group, euthymic animals infected on day 14 versus 30 (P = .06); euthymic versus thymectomized animals infected on day 30 (P = .04). In BM + Tcon + Treg group, euthymic animals infected on day 14 versus 30 (P = 1.0); euthymic versus thymectomized animals infected on day 30 (P = .08).